The present invention relates to a method and apparatus for welding a fastener to a metal member for assembling automotive vehicle structures.
It is known that the manufacture of automotive vehicles often requires that a metal fastener be attached to a metal member to form an automotive vehicle structure. As an example, it is often desirable that a metal nut with a substantially cylindrical through-hole be welded to a metal sheet with a corresponding through-hole such that the through-holes of the nut and sheet are coaxially aligned. Such an arrangement allows a bolt or other fastener to extend at least partially through the through-holes of both the nut and the sheet.
Projection welding is one potential method of attaching a fastener to a member. Projection welding typically requires the metal fastener to include one or more protrusions, which are contacted with the metal member. Thereafter, electrodes pass a current through the member, the fastener and the protrusions to heat and soften the protrusions. In turn, the protrusions bond to the member for welding the fastener to the member.
Conventional projection welding processes, however, present several drawbacks. For example, several different tools may be required to position the fastener and member relative to the electrodes, depending upon the sizes and configurations of the fastener, the member or both. Weld consistency and strength may be less than optimal if the various tools are not properly used for welding fasteners and members of corresponding size. Moreover, conventional processes may not provide any automatic assurances that the fastener is welded to the member. Additionally, electrodes and other tools used for welding the fastener to the member may be rapidly worn or damaged. Thus, there is a need for improved projection welding techniques, instruments or both, for overcoming one or more of the above drawbacks and for achieving high integrity attachment of metal fasteners to metal members.
The present invention meets these needs by providing an improved apparatus and method of projection welding a metal fastener to a metal member, with particular utility in the formation of components for an automotive vehicle. The apparatus includes a first electrical contact with a cavity defined therein for correspondingly (e.g., matingly) fitting about at least a partial outer perimeter of the fastener, the cavity being at least partially defined by an inner annular surface of the first contact. The apparatus also includes an outer annular housing having a forward end portion, a rearward end portion, and a central portion defining an internal opening extending internally along a length of the housing. The forward end portion supports a second electrical contact. The internal opening includes a first chamber adjacent the forward portion and a second chamber adjacent the rearward portion and an elongated tunnel intermediate the first and second chambers. Additionally, the forward end portion and the second contact cooperatively define a through-hole of the opening.
The apparatus further includes a piston assembly including a piston and pin disposed within the opening of the housing. The piston includes a first forward end adjacent the forward end portion of the housing and a second rearward end adjacent the rearward end portion of the housing. The pin includes an inner cylindrical steel core surrounded by an annular insulator. The insulator is formed of a ceramic material and the insulator is thinner about the core at a free end of the pin for forming a shoulder thereon. Preferably, the apparatus includes at least one pressurized fluid source in fluid communication with the first and second chambers for translating the pin and piston assembly between an extended position, an intermediate position and a retracted position. It is also preferable for the apparatus to include a first sensor adjacent to the first chamber and a second sensor adjacent to the second chamber, wherein the first and second switches monitor whether the pin and piston assembly are in the extended position, the intermediate position or the retracted position.
In operation, an electrical energy source is electrically connected to the first electrical contact and the second electrical contact for passing a current between the contacts and through a plurality of protrusions of the fastener. Moreover, a control unit is in communication with the sensores, the electrical energy source and the fluid source for determining whether the pin and piston assembly have been successfully moved to the intermediate position for welding and for determining whether the pin and piston assembly have been successfully moved to the retracted position for removal of the fastener and member.
The method of projection welding a metal fastener to a metal member, begins by providing a projection welding apparatus having a first electrical contact and a locator assembly including a piston assembly, at least one sensor and a copper housing, wherein the housing substantially surrounds the piston assembly and supports a second electrical contact. A member is then positioned upon the locator assembly wherein a first surface of the member abuttingly contacts the second electrical contact and a pin of the piston assembly extends through a through-hole in the member. A fastener is positioned upon a pin of the piston assembly such that the fastener is spaced away from the member. The fastener is contacted the with the first electrical contact, which urges the fastener toward the member such that the piston assembly moves from the extended position to an intermediate position and such that a plurality of protrusions of the fastener contact a second surface of the member. The fastener is then welded to the member by passing a current between the electrical contacts and through the protrusions of the fastener if the at least one sensor senses that the piston assembly has been successfully moved to the intermediate position. Thereafter, the first electrical contact is retracted and the piston assembly is moved to a retracted position and removal of the member and fastener is signaled if the at least one sensor senses that the piston assembly remains in the intermediate position after retraction of the first electrical contact.
The present invention thus provides an improved projection welding apparatus and projection welding technique for consistently attaching metal fasteners to metal members with high structural integrity welds.